System, Method and Apparatus for Composite Seal Gland Insert in Roller Cone Rock Bit

ABSTRACT

A composite seal gland insert for a roller cone rock bit is a polymer composite sleeve containing one or more constituents that function to significantly lower the wear of the elastomeric seal ring. A fluid lubricant film also may be used between the elastomer seal and the gland. The outer surface of the insert is profiled to provide a sealing surface against which the elastomer seal runs. The insert is installed over the bearing pin and has a surface that engages the last machined surface of the leg. A static seal, which may comprise an additional elastomeric seal, may be used beneath the gland insert to provide a pressure seal between the insert and the pin. An adhesive also may be used as the pressure seal and also to retain the gland insert in the desired position. In addition, a mechanical anti-rotation device may be used to prevent rotation of the gland insert.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates in general to roller cone rock bits and, in particular, to an improved system, method and apparatus for a composite seal gland insert for enhancing the seal between the bearing pins and the roller cones on a roller cone rock bit.

2. Description of the Related Art

In roller cone rock bits, wear of the elastomer rotary bearing seals between the bearing pins and the roller cones is a primary cause of seal failure. Elastomer seals in current roller cone bits typically run in glands made up by opposing recesses that are formed on the bearing pin and on the inner surface of the cone. Wear occurs on both the elastomer seal itself and on the steel gland counter face surfaces that are in sliding contact with the elastomer seal. However, the majority of the wear typically occurs on the elastomer seal surface. The loss of seal radial cross-section as well as the loss of the seal contacting surface design geometry reduces sealing efficiency as there is a reduction in overall sealing pressure and a change in the distribution of the sealing pressure on the contacting surfaces. Consequently, there is an increased probability of drilling fluid ingress into the bearing, which leads to rapid bearing failure. An improved solution that overcomes the limitations and problems of prior art designs would be desirable.

SUMMARY OF THE INVENTION

Embodiments of a system, method, and apparatus for a composite seal gland insert in a roller cone rock bit are disclosed. Wear of the elastomer seal is reduced by reducing the friction between the seal and mating gland surface. In one embodiment, the steel seal gland surface is supplemented with the seal gland insert. The insert comprises a polymer composite sleeve containing one or more constituents that function to significantly lower the friction compared to direct engagement with the steel seal gland. The seal gland insert may comprise a thermoplastic polymer such as polyetheretherketone (PEEK) or a polyimide. Preferably, the polymer material contains a reinforcing material such as carbon fiber. Also, preferably the polymer contains a low friction additive such as polytetrafluorethylene (PTFE), which is impregnated into the composite material.

In one embodiment, a fluid lubricant film is provided between the elastomeric seal and the composite gland for initial operation. Subsequently, during operation, the grease or lubricant of the bit will enter the spaces between the elastomeric seal and the composite gland. In one embodiment, the outer surface of the composite gland insert is profiled with a grooved pattern against which the elastomer seal runs. The insert is installed over the pin and one surface is located against the last machined surface of the leg. A static seal, which may comprise an additional elastomeric o-ring seal, may be used beneath the gland insert to provide a pressure seal between the insert and the pin. Alternatively, a suitable adhesive may be used to retain the gland insert in the desired position. The adhesive may provide the pressure seal between the insert and the pin. If desired, a mechanical anti-rotation device also may be used to inhibit rotation of the gland insert.

The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the features and advantages of the present invention are attained and can be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings. However, the drawings illustrate only some embodiments of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.

FIG. 1 is an isometric view of one embodiment of a roller cone rock bit constructed in accordance with the invention;

FIG. 2 is a sectional view of one embodiment of a leg of a roller cone rock bit constructed in accordance with the invention;

FIG. 3 is an enlarged sectional view of one embodiment of a lower portion of a seal assembly on a leg of a roller cone rock bit constructed in accordance with the invention; and

FIG. 4 is an enlarged sectional view of the insert employed in the seal assembly of FIG. 3.

FIG. 5 is an enlarged view of a portion of the outer diameter of the insert of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1-5, embodiments of a system, method and apparatus for a composite seal gland insert for enhancing the seal between the bearing pins and the roller cones on a roller cone rock bit are disclosed. FIGS. 1 and 2 illustrate a rock bit 11 having a body 13 with a threaded upper end for attachment to the lower end of a drill string. Body 13 has at least one bit leg 15 (typically three) that extend downward from it. Each bit leg 15 has a bearing pin 17 (FIG. 2) that extends downward and inward along an axis 16. Bearing pin 17 has an outer end, referred to as the last machined surface 19, where it joins bit leg 15.

In one embodiment, bearing pin 17 has a main journal surface 18 and a nose 21 having a smaller diameter than surface 18 that is formed on its inner end. Nose 21 also has a pilot pin radial bearing surface 22 that is parallel to surface 18 relative to axis 16. In another embodiment (e.g., for larger diameter bits), roller bearings may be used instead of journal bearings. The invention is well suited for both types of applications.

A roller cone 23 is rotatably mounted to bearing pin 17. Cone 23 has a plurality of protruding cutting elements 25. Cone 23 has a cavity 27 that is slightly larger than the outer diameters of bearing pin 17. Cone 23 may be retained in more than one manner. In the embodiment shown, cone 23 is retained on bearing pin 17 by a plurality of balls 33 that engage a mating annular recess formed in cone cavity 27 and on bearing pin 17. Balls 33 lock the roller cone 23 to bearing pin 17 and are inserted through a ball passage 35 during assembly after cone 23 is placed on bearing pin 17. Ball passage 35 extends to the exterior of bit leg 15 and may be plugged as shown after balls 33 are installed.

In the embodiment shown, a portion of cavity 27 slidingly engages journal surfaces 18 and 22. In one embodiment, the outer end of journal surface 18 is considered to be at a junction with the gland area engaged by a seal assembly 31, and the inner end of journal surface 18 is considered to be at the junction with the groove or race for balls 33. Journal surfaces 18 and 22 serve as a journal bearing for loads imposed along the axis of bit 11. Again, other types of drill bits may utilize roller bearings instead of journal bearing surfaces and are readily configured for the invention.

In a sealed lubricated bearings embodiment, a lubricant port 37 is located on an exterior portion of journal surface 18 of bearing pin 17. The port 37 is connected to a passage 39 via ball passage 35. Passage 39 leads to a lubricant reservoir 41 that contains a lubricant. Lubricant reservoir 41 may be of a variety of types. In one embodiment, an elastomeric diaphragm 43 separates lubricant in lubricant reservoir 41 from a communication port 45 that leads to the exterior of bit body 13. Communication port 45 communicates the hydrostatic pressure on the exterior of bit 11 with pressure compensator 43 to reduce and preferably equalize the pressure differential between the lubricant and the hydrostatic pressure on the exterior.

Cone 23 also has a back face 29 that is located adjacent, but not touching, last machined surface 19. A seal assembly 31 is located in a seal cavity adjacent to the back face 29. As shown in the embodiment of FIG. 3, the seal assembly 31 is located in a gland 51 formed between the bearing pin 17 and cone 23 adjacent to the last machined surface 19. In one embodiment, the seal assembly 31 comprises an elastomeric or dynamic seal 53 that is located in gland 51 in roller cone 23 for rotation with cone 23. In this version, the dynamic seal 53 is axially spaced apart and free of contact with the last machined surface 19. In this embodiment, gland 51 comprises a groove formed in cone cavity 37, having flat sidewalls on opposite sides of dynamic seal 53. In an alternate embodiment, gland 51 has only a single, outward facing sidewall. Dynamic seal 53 may be a conventional seal used in rolling cone bits. In this embodiment, it has a greater radial thickness from its inner radius to its outer radius than its axial width.

The seal assembly 31 also comprises a gland insert 55 that is a ring located in the gland 51 between the dynamic seal 53 and the bearing pin 17. In other embodiments, however, the positions may be reversed such that the gland insert 55 engages only the cone 23 and the dynamic seal 53 engages the bearing pin 17. In some embodiments, the gland insert 55 engages the last machined surface 19, and no portion of the gland insert 55 engages the roller cone 23. Dynamic seal 53 engages gland 51 in sliding or dynamic engagement in all of the embodiments. Gland insert 55 is generally rectangular in cross-section in this embodiment and has a beveled corner on its outer edge that engages the rounded intersection of last machined surface 19 and bearing pin 17.

The gland insert may comprise a polymer composite sleeve that reduces wear of the elastomer seal by reducing the friction between it and the mating gland surface. The gland insert may contain one or more constituents that function to significantly lower the friction compared to direct engagement with the steel seal gland. The term “composite” is used herein to mean a polymer material containing a reinforcing material that is dispersed through at least a part thereof and structurally joined with the polymeric material. For example, composite gland insert 55 may comprise a thermoplastic polymer such as polyetheretherketone (PEEK) or a polyimide as the matrix material. The reinforcing material 56 (FIG. 4) may be carbon fiber or glass fiber. The composite gland insert may also contain a low friction additive such as polytetrafluorethylene (PTFE). The low friction material is dispersed within the polymer matrix in a known manner. The dispersed low friction material extends at least 0.050 inch from the outer diameter inward into gland insert 55 or may be throughout gland insert 55.

Composite gland insert 55 must be capable of withstanding the elevated temperatures that occur during drilling. Typically, dynamic seal 53 is of a rubber-based material that may withstand about 375 degrees F. without significant degradation. Preferably composite gland insert 55 is capable of withstanding about 400-500 degrees F. without significant degradation. Gland insert 55 is much harder and less resilient than composite dynamic seal 53. For example, the tensile strength in teems of pounds per square inch of gland insert 55 may be ten times or more greater than the tensile strength of dynamic seal 53. The inner diameter of gland insert 55 is preferably only slightly greater than the outer diameter of journal 18, for example about 0.002 to 0.005 inch. Consequently, gland insert 55 may be considered to be rigidly mounted on journal 18 so that it is not axially movable relative to journal 18.

In still other embodiments, the surface of gland insert 55 that engages dynamic seal 53, which is the outer diameter of insert 55 in this example, is profiled to enhance lubrication. As illustrated in FIG. 5, the profile may comprise wavy or sinusoidal grooves 60. Alternately, grooves 60 could be helical, chevron-shaped or other patterns. In addition, as shown in FIG. 3, seal assembly 31 may further comprise a static seal 61 located between the inner diameter of gland insert 55 and the bearing pin 17. Static seal 61 provides a pressure seal to prevent lubricant leakage and/or drilling fluid ingress beneath seal gland insert 55. Static seal 61 may be a ring of a rubber-based material seated within a recess 63 within the inner diameter of gland insert 55. Static seal 61 has a cross-sectional dimension that is much smaller than the cross-sectional dimension of dynamic seal 53. For example, it may have a circular cross-section with a diameter less than 0.020 inch. Additionally, a static seal arrangement may retain gland insert 55 so as to keep it from rotating around journal 18. For example, the static seal arrangement may comprise an adhesive rather than an elastomeric ring.

Adhesive, if employed, may serve also to prevent gland insert 55 from rotating around journal 18. Alternately, a mechanical anti-rotation device 65 (e.g., a pin, as shown in FIG. 3) extends from last machined surface 19 and engages a notch in gland insert 55 to prevent rotation of the gland insert 55 relative to the bearing pin 17.

While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention. 

1. A rock bit, comprising: a body having a bit leg extending therefrom; a bearing pin extending from the bit leg and having a bearing pin axis, a last machined surface adjacent the bit leg; a roller cone rotatably mounted to the bearing pin; a gland defined between the bearing pin and the roller cone adjacent the last machined surface; an elastomer seal located in the gland; and a gland insert located in the gland between the elastomer seal and one of the bearing pin and the roller cone, the gland insert being formed from a polymer material.
 2. The rock bit according to claim 1, wherein the polymer material comprises a polymer composite material having a reinforcing material dispersed within.
 3. The rock bit according to claim 2, wherein the reinforcing material comprises fibers within the polymer material.
 4. The rock bit according to claim 3, wherein the fiber comprises carbon fiber.
 5. The rock bit according to claim 1, wherein the polymer material comprises one of polyetheretherketone (PEEK) and a polyimide.
 6. The rock bit according to claim 1, wherein the polymer material has a low friction material dispersed within at least a part thereof.
 7. The rock bit according to claim 1, wherein a surface of the gland insert that engages the elastomer seal has a grooved profile.
 8. The rock bit according to claim 1, wherein the gland insert is installed on the bearing pin, and a surface of the gland insert engages the last machined surface.
 9. The rock bit according to claim 1, further comprising a static seal between the gland insert and said one of the bearing pin and the roller cone.
 10. The rock bit according to claim 1, further comprising a mechanical anti-rotation device extending between the gland insert and the last machined surface to prevent rotation of the gland insert relative to the bearing pin.
 11. A rock bit, comprising: a body having a bit leg extending therefrom; a bearing pin extending from the bit leg and having a bearing pin axis, a last machined surface adjacent the bit leg; a roller cone rotatably mounted to the bearing pin; a gland defined between the bearing pin and the roller cone adjacent the last machined surface; an elastomer seal located in the gland and engaging the roller cone; and a gland insert located in the gland between the elastomer seal and the bearing pin, the elastomer seal slidingly engaging an outer diameter of the gland insert, the gland insert comprising a sleeve formed of a polymer composite material containing a reinforcing material therein.
 12. The rock bit according to claim 11, wherein the polymer composite material comprises one of polyetheretherketone (PEEK) and a polyimide.
 13. The rock bit according to claim 11, wherein the outer diameter of the gland insert contains a grooved profile.
 14. A rock bit, comprising: a body having a bit leg extending therefrom; a bearing pin extending from the bit leg and having a bearing pin axis, a last machined surface adjacent the bit leg; a roller cone rotatably mounted to the bearing pin; a gland defined between the bearing pin and the roller cone adjacent the last machined surface; an elastomer seal located in the gland and engaging the roller cone for rotation with the roller cone; a gland insert located in the gland between the elastomer seal and the bearing pin, the gland insert being a sleeve mounted on the bearing pin with an anti-rotation device to prevent any rotational movement of the gland insert relative to the bearing pin, the elastomer seal being in sliding engagement with an outer diameter of the gland insert; a static seal of elastomeric material between an inner diameter of the gland insert and the bearing pin; and the gland insert being formed of a polymer containing reinforcing fibers and having a low friction material therein.
 15. The rock bit according to claim 14, further comprising a mechanical anti-rotation device extending between the gland insert and the bit leg.
 16. The rock bit according to claim 14, wherein the reinforcing fibers are formed of carbon.
 17. The rock bit according to claim 14, wherein the polymer comprises a selected one of polyetheretherketone (PEEK) and a polyimide.
 18. The rock bit according to claim 14, wherein the gland insert has a greater tensile strength than a tensile strength of the elastomer seal. 